Organometallic adduct compounds

ABSTRACT

The invention relates to the use of stabilised organometallic adduct compounds for the production of thin films and epitaxic layers by gas phase deposition.

The invention relates to the use of organometallic adduct compoundscontaining, as metals, aluminium, gallium or indium, for the productionof thin films or of epitaxic layers by gas phase deposition, and to newadducts containing gallium or indium.

The deposition of such layers either from pure elements of the thirdgroup or from combinations with other elements, such as, for example,gallium arsenide, indium phosphide or gallium phosphide, can be used forthe production of electronic and optoelectronic switching elements,compound semiconductors and lasers. The deposition of these layers iseffected from the gas phase.

The properties of these films depend on the deposition conditions and onthe chemical composition of the film deposited.

All the known methods, such as the metal-organic chemical vapourdeposition (MOCVD) method, the photo-metal-organic vapour phase(photo-MOVP) method in which the substances are decomposed by UVirradiation, the laser-chemical vapour deposition (laser CVD) method orthe metal-organic magnetron scattering (MOMS) method, are suitable fordeposition from the gas phase. The advantages compared with othermethods are a controllable growth of the layer, an accurate dopingcontrol and also easy handling and convenience of production because ofthe normal pressure or low-pressure conditions.

In the MOCVD method organometallic compounds which decompose at atemperature below 1100° C. with deposition of the metal are employed.Typical apparatus used at present for MOCVD consists of a "bubbler"having a feeder for the organometallic component, a reaction chambercontaining the substrate to be coated and a source of a carrier gaswhich should be inert towards the organometallic component. The"bubbler" is kept at a constant, relatively low temperature which ispreferably above the melting point of the organometallic compound, butfar below its decomposition temperature. The reaction chamber ordecomposition chamber is preferably at a very much higher temperature,which should be below 1100° C., at which the organometallic compound iscompletely decomposed and the metal is deposited. The organometalliccompound is brought into the vapour state by means of the carrier gasand is admitted into the decomposition chamber together with the carriergas. The mass flow of the vapour can be controlled easily and thuscontrolled growth of the thin layers is also possible.

Hitherto metal alkyls, such as, for example, trimethylgallium,trimethylaluminium or trimethylindium, have been mainly used for gasphase deposition. However, these compounds are extremely sensitive tothe air and self-ignitable and in some cases can decompose even at roomtemperature. Involved precautions are therefore necessary for thepreparation, transport, storage and use of these compounds. Some rathermore stable adducts of metal alkyls with Lewis bases, such as, forexample, trimethylamine and triphenylphosphine, are also known (forexample are described in British Patent 2,123,422, EP-A 108,469 or EP-A176,537), but these have only a limited suitability for gas phasedeposition because of their low vapour pressure.

However, in contrast with the adduct compounds to be used in accordancewith the invention, these known adducts do not contain hydrogen atoms asa radical on the V element.

Organometallic compounds suitable for the MOCVD technique are known fromGerman Offenlegungsschrift 3,631,469. The compounds described thereinare, however, not adducts, but compounds which have been stabilisedwithin the molecule.

It was therefore the object of the present invention to findorganometallic adduct compounds which are simple to handle and stable atroom temperature and which have a sufficiently high vapour pressure tobe enabled to decompose from the gas phase and are consequently suitablefor the various methods of gas phase deposition.

It has now been found that organometallic adduct compounds of the thirdand fifth main group, the compound of the fifth main group containingone or two hydrogen atoms, are excellently suitable for gas phasedeposition.

These adducts have a decisive advantage over the organometallic adductshitherto used and known, which have the structure R₃ MXR₃ and thuscontain only alkyl or aryl groups.

The adducts according to the invention, which have at least one H atomon the element of the fifth main group, react at fairly hightemperatures (>100° C.) with the release of R*H (R* being R¹, R² or R³)to give compounds of the structure R*₂ MXR⁴ R⁵. In these compounds theMX bond can be regarded as weak compared with the groups attached to themetal of the third main group, and thus the group XR⁴ R⁵ constitutes avery good detachable group. In the MOCVD process, therefore, thesubstance R*₂ MXR⁴ R⁵ produced in situ on the hot wafer leads to areduced incorporation of carbon.

Stabilised adducts of this type have in part been described, but only inconnection with structural investigations, investigations of complexformation or stability investigations. In part, the compounds of theformula I are also new.

The invention therefore relates to the use of organometallic adductcompounds of the formula I ##STR1## wherein M is aluminium, gallium orindium, X is nitrogen, phosphorus, arsenic or antimony, R¹, R², R³ andR⁴ independently of one another are each H, an alkyl group which has 1-8C atoms and which can also be partly or completely fluorinated, acycloalkyl, alkenyl or cycloalkenyl group having 3-8 C atoms in eachcase or an aryl group, and R⁵ is an alkyl group which has 1-8 C atomsand which can also be partly or completely fluorinated, a cycloalkyl,alkenyl or cycloalkenyl group having 3-8 C atoms in each case or an arylgroup, as starting materials for the production of thin films orepitaxic layers by gas phase deposition and to a process for thepreparation of thin films or epitaxic layers by gas phase depositionfrom organometallic compounds, in which process the organometalliccompounds employed are the compounds of the formula I. The inventionalso relates to the introduction, in the process according to theinvention, of one or more compounds of arsenic, antimony or phosphoruswhich are gaseous under the reaction conditions used, in the course ofthe deposition process.

The invention also relates to the new adducts of the formula Icorresponding to the formula II ##STR2## wherein M' is gallium orindium, X is nitrogen, phosphorus, arsenic or antimony, R¹, R², R³ andR⁴ independently of one another are each H, an alkyl group which has 1-8C atoms and which can also be partly or completely fluorinated, acycloalkyl, alkenyl or cycloalkenyl group having 3-8 C atoms in eachcase, or an aryl group and R⁶ is a branched alkyl group which has 3-8 Catoms and which can be partly or completely fluorinated.

The stability of the adducts of the formulae I and II is based on thetransfer of electrons from the nitrogen, phosphorus, arsenic or antimonyatom onto the electron-deficient IIIB element. These adducts thereforedisplay a high stability to air and oxygen, they are no longerself-ignitable and they are therefore easy to handle.

In the gas phase, however, the compounds according to the invention canbe decomposed readily with deposition of the metal. Since the compoundsof the formulae I and II contain stable detachable groups which can besplit off readily, the result is a lower incorporation of carbon, whichhas great advantages for the quality of the end products.

The films deposited can be formed either from the pure IIIB element orfrom a combination with elements of the fifth group, on any desiredsubstrates. Depending on the substrate and the deposition technique,they can be of an epitaxic nature. Many of the adducts of the formulae Iand II are therefore also particularly suitable for the MOCVD method,since they are present as monomers and therefore in most cases asliquids at room temperature.

The adducts of the formulae I and II have a vapour pressure which issuitable for the MOCVD technique and they are therefore excellentlysuitable for use as starting materials.

In the formula I, M is aluminium (Al), gallium (Ga) or indium (In),preferably Ga or In.

The new adducts of the formula II wherein M' is Ga or In areparticularly preferred compounds of the formula I.

X in the formulae I and II is nitrogen as a first preference orphosphorus or arsenic as a second preference.

The radicals R¹, R², R³ and R⁴ in the formulae I and II are preferablyeach H or a linear or branched alkyl group having 1-8 C atoms,preferably 1-5 C atoms. The alkyl groups are preferably linear andaccordingly are preferably methyl, ethyl, propyl, butyl, pentyl and alsohexyl, heptyl, octyl, isopropyl, sec.-butyl, tert.-butyl,2-methylpentyl, 3-methylpentyl or 2-octyl. The alkyl radicals can bepartly or completely fluorinated and are, for example, monofluoromethyl,trifluoromethyl, difluoroethyl, trifluoroethyl, pentafluoroethyl ortrifluoropropyl. Preferably, only one of the radicals R¹, R², R³ or R⁴is H.

If R¹, R², R³ and/or R⁴ are a cycloalkyl or cycloalkenyl group having3-8 C atoms, they are preferably cyclopropyl, cyclobutyl, cyclopentyl,cyclopentenyl, cyclohexyl, cyclohexenyl, cyclohexadienyl, cycloheptyl,cycloheptenyl, cycloheptadienyl, cyclooctyl, cyclooctenyl,cyclooctadienyl, cyclooctatrienyl or cyclooctatetraenyl.

R¹, R², R³ and/or R⁴ are preferably also alkenyl groups having 3-8 Catoms, preferably 3-5 C atoms. Accordingly they are preferably propenyl,butenyl, pentenyl and also hexenyl, heptenyl or octenyl.

Furthermore, compounds of the formulae I and II wherein R¹, R², R³and/or R⁴ are an aryl group are preferred. In this regard aryl ispreferably synonymous with a phenyl group. This phenyl group can alsocontain substituents. Since these substituents exert no appreciableeffect on the desired end use, any substituents which have nointerfering effect on the decomposition reaction are allowed.

R⁵ in formula I is preferably an alkyl group having 1-8 C atoms,preferably 1-5 C atoms. It can be linear or branched, but is preferablybranched and, accordingly, is preferably isopropyl, sec.-butyl,tert.-butyl and also preferably 2-methylpentyl, 3-methylpentyl, 2-octyl,methyl, ethyl, propyl, butyl, hexyl, heptyl or octyl.

The alkyl radical in R: can also be partly or completely fluorinated andis then preferably monofluoromethyl, trifluoromethyl, difluoroethyl,trifluoroethyl, pentafluoroethyl or trifluoropropyl.

If R⁵ is a cycloalkyl or cycloalkenyl group or an alkenyl group,preferred groups are those which are also indicated as preferred for R¹-R⁴.

R⁶ in formula II is a branched alkyl group which has 3-8 C atoms,preferably 3-5 C atoms, and which can also be partly or completelyfluorinated. R⁶ is, accordingly, preferably isopropyl, sec.-butyl,tert.-butyl, 1-methylbutyl, 2-methylbutyl, 1,2-dimethylpropyl and also2-methylpentyl, 3-methylpentyl, 2-octyl or 2-hexyl.

The new adducts of the formula II thus contain at least one branchedalkyl group and at least one hydrogen atom in the moiety containing theelement of the fifth group.

Compounds of the formula II belonging to the following groups areparticularly preferred:

(methyl)₃ Ga NH (isopropyl)₂

(ethyl)₃ Ga NH (isopropyl)₂

(methyl)₃ In NH (isopropyl)₂

(ethyl)₃ In NH (isopropyl)₂

(methyl)₃ Ga-AsH₂ (isopropyl)

(methyl)₃ Ga-AsH (isopropyl)₂

(ethyl)₃ Ga-AsH₂ (tert.-butyl)

(ethyl)₃ Ga-NH (sec.-butyl)₂

R¹ R² R³ Ga NH₂ (tert.-butyl)

R¹ R² R³ Ga NH₂ (2-octyl)

R¹ R² R³ Ga NH₂ (2-methylpentyl)

R¹ R² R³ In PH (isopropyl)₂

R¹ R² R³ In PH₂ (isopropyl)

R¹ R² R³ In PH (sec.-butyl)₂

R¹ R² R³ In PH (tert.-butyl)₂

R¹ R² R³ In PH₂ (3-methylpentyl)

R¹ R² R³ In NH₂ (tert.-butyl)

R¹ R² R³ In NH (2-octyl)₂

These compounds are also preferred adducts of the formula I. Thefollowing are further preferred adducts of the formula I:

(methyl)₃ Al NH (ethyl)₂

(methyl)₃ Al NH₂ (ethyl)

(ethyl)₃ Al NH (ethyl)₂

(ethyl)₃ Al NH (isopropyl)₂

(methyl)₃ Al NH (cyclohexyl)₂

(propyl)₃ Al NH₂ (methyl)

(ethyl)₃ Ga NH (ethyl)₂

(ethyl)₃ In NH (methyl)₂

(ethyl)₃ Ga NH₂ (phenyl)

(ethyl)₃ Ga AsH (pentyl)₂

(methyl)₃ Ga AsH₂ (butyl)

(isopropyl)₃ In PH (ethyl)₂

(ethyl)₃ In PH (phenyl)₂.

The compounds of the formulae I and II are excellently suitable forMOCVD epitaxy or the MOCVD method, since they decompose at elevatedtemperatures with liberation of the corresponding metal. They are alsosuitable for the other methods of gas phase deposition, such asphoto-MOVP, laser-CVD or MOMS.

The compounds of the formulae I and II are prepared by methods known perse, such as are described in the literature (for example G. Bahr, P.Burba, Methoden der organischen Chemie ("Methods of organic chemistry"),Volume XIII/4, Georg Thieme Verlag, Stuttgart (1970)), specificallyunder reaction conditions which are known and suitable for the reactionsmentioned. In this regard it is also possible to make use of variantswhich are known per se but are not mentioned here in detail.

For example, the adducts can be prepared by direct reaction ofappropriate compounds of the III elements (R¹ R² R³ M or R¹ R² R³ M')with the compounds containing the element of the fifth group (XHR⁴ R⁵ orXHR⁴ R⁶ ). Another possible means is to react an appropriate etherderivative of the III compound with the fifth compound, in the course ofwhich a ligand exchange takes place (for example the exchange alreadydescribed by G. Bahr, P. Burba, Houben-Weyl, Volume 13/4, page 338,Georg Thieme Verlag, Stuttgart (1970)).

In the process according to the invention for the production of thinfilms or epitaxic layers on any desired substrates, the stabilisedorganometallic adduct compounds of the formula I are employed asstarting compounds in the gas phase deposition processes, known per se,of organometallic compounds. The reaction conditions can be chosenanalogously to the values known from the literature and familiar tothose skilled in the art.

In order to produce compound semiconductors or electronic andoptoelectronic components, one or more compounds of arsenic, antimony orphosphorus which are gaseous under the reaction conditions used, forexample AsH₃, As(CH₃)₃, PH₃ or SbH₃, can be added in addition, in theprocess according to the invention, during the deposition process in thedecomposition chamber. A further variant of the process according to theinvention consists in adding doping agents during the deposition processin addition to the organometallic adducts, according to the invention,of the formula I. Doping agents employed in this regard are volatileorganometallic compounds of iron, magnesium, zinc or chromium. Examplesof compounds considered to be preferred in this regard are Zn(CH₃)₂,Mg(CH₃)₂ or Fe(C₅ H₅)₂.

It is also possible to add the compounds of the formula I as dopingagents during the process of depositing other organometallic compounds.

The layers produced by the process according to the invention can beused for the production of electronic and optoelectronic switchingelements, compound semiconductors or lasers.

Since only approx. 1-10 % of the free metal alkyls employed can, forthermodynamic reasons, be deposited on the substrate as an epitaxiclayer in the epitaxy equipment in use at the present time, thedestruction of the excess metal alkyls, which cannot be recoveredbecause of their extreme sensitivity, constitutes a considerableproblem. Because of their high stability, however, the compounds,according to the invention, of the formula I open up new possibilitiesfor the safe destruction or recovery of the valuable IIIB compounds.

The following examples are intended to illustrate the invention ingreater detail without limiting it. Temperature data are given indegrees centigrade or Kelvin. M.p. means melting point and b.p. meansboiling point.

Example 1

270 g (0.27 mol) of diisopropylamine are added to 30.6 g (0.27 mol) oftrimethylgallium diethyl etherate. The ether is then removed bydistillation and the product is fractionally distilled. This gives(methyl)₃ Ga NH (isopropyl)₂ of b.p. 138° C.

The following are prepared analogously:

(methyl)₃ Ga NH (propyl)₂

(methyl)₃ Ga NH (sec.-butyl)₂

(methyl)₃ Ga NH (tert.-butyl)₂

(methyl)₃ Ga NH₂ (ethyl)

(methyl)₃ Ga NH₂ (isopropyl)

(ethyl)₃ Ga NH (isopropyl)₂

(ethyl)₃ Ga NH (propyl)₂

(ethyl)₃ Ga NH (sec.-butyl)₂

(ethyl)₃ Ga NH (tert.-butyl)₂

(ethyl)₃ Ga NH₂ (methyl)

(ethyl)₃ Ga NH₂ (isopropyl)

(methyl)₃ Ga NH (phenyl)₂

Example 2

(Methyl)₃ In NH(isopropyl)₂ of b.p. 69° at 10 mbar is obtainedanalogously to Example 1 by reacting 61.0 g (0.26 mol) oftrimethylindium diethyl etherate and 101.0 g (0.26 mol) ofdiisopropylamine at 20°.

The following are prepared analogously:

(methyl)₃ In NH (propyl)₂

(methyl)₃ In NH (ethyl)₂

(methyl)₃ In NH (sec.-butyl)₂

(methyl)₃ In NH (tert.-butyl)₂

(methyl)₃ In NH₂ (ethyl)

(methyl)₃ In NH₂ (isopropyl)

(ethyl)₃ In NH (isopropyl)₂

(ethyl)₃ In NH (propyl)₂

(ethyl)₃ In NH (ethyl)₂

(ethyl)₃ In NH (phenyl)₂

(ethyl)₃ In NH (sec.-butyl)₂

(ethyl)₃ In NH₂ (methyl).

Example 3

Use of the (methyl)₃ GaNH(isopropyl)₂ adduct for epitaxy.

The (methyl)₃ GaNH(isopropyl)₂ adduct was used for epitaxy together withAsH₃ in a low-pressure MOCVD apparatus (1000-2000 Pa). The growthtemperatures were between 850° K. and 1050° K. The electron mobility at77° K. of the GaAs layer produced by epitaxy was μ₇₇ =51000 cm² /Vs.Incorporation of nitrogen was not observed.

We claim:
 1. Organometallic adduct compounds of the fomula II ##STR3##wherein M' is gallium or indium, X is nitrogen, phosphorus, arsenic orantimony, R¹, R², R³ and R⁴ independently of one another are each H, analkyl group which has 1-8 C atoms and which can also be partly orcompletely fluorinated, a cycloalkyl, alkenyl or cycloalkenyl grouphaving 3-8 C atoms in each case, or an aryl group and R⁶ is a branchedalkyl group which has 3-8 C atoms and which can be partly or completelyfluorinated.
 2. A process for the production of thin films or layersfrom organometallic adduct compound by gas phase deposition, whereinsaid organometallic adduct compounds are of the formula I ##STR4##wherein: M is aluminum, gallium, or indium;X is nitrogen, phosphorus,arsenic, or antimony; R¹, R², R³, and R⁴ are each, independently of eachother, H, a C₁₋₈ -alkyl group, a partly or completely fluorinated C₁₋₈-alkyl group, or a C₃₋₈ -alkenyl group; R⁵ is a C₁₋₈ -alkyl group, apartly or completely fluorinated C₁₋₈ -alkyl group, or a C₁₋₃ -alkenylgroup.
 3. A process according to claim 2, wherein said thin films orlayers are epitaxic layers.
 4. A process according to claim 2, whereindoping agents are further introduced during said gas phase deposition.5. A process according to claim 2, wherein said organometallic adductcompound of the formula I is (methyl)₃ GaNH(isopropyl)₂.
 6. A processaccording to claim 2, wherein said organometallic adduct compound of theformula I is (methyl)₃ InNH(isopropyl)₂.
 7. A process according to claim2, wherein said organometallic adduct compound of the formula I is(ethyl)₃ GaNH(isopropyl)₂.
 8. In a process for the production of asemiconductor, electronic, or optoelectronic component or a laser,comprising producing a thin film or layer from an organometallic adductcompound by gas phase deposition, the improvement wherein the compoundhas formula I ##STR5## wherein: M is aluminum, gallium, or indium;X isnitrogen, phosphorus, arsenic, or antimony; R¹, R², R³, and R⁴ are each,independently of each other, H, a C₁₋₈ -alkyl group, a partly orcompletely fluorinated C₁₋₈ -alkyl group, or a C₃₋₈ -alkenyl group; R⁵is a C₁₋₈ -alkyl group, a partly or completely fluorinated C₁₋₈ -alkylgroup, or a C₁₋₃ -alkenyl group, and at least one gaseous compound ofarsenic, antimony, or phosphorus is introduced during said gas phasedeposition.
 9. A process according to claim 8, wherein the at least onecompound of arsenic, antimony, or phosphorus is AsH₃, As(CH₃)₃, or SbH₃.10. A process of producing thin films or layers by gas phase depositionfrom organometallic adduct compounds, comprising adding doping agents ofthe formula I ##STR6## wherein: M is aluminum, gallium, or indium;X isnitrogen, phosphorus, arsenic, or antimony; R¹, R², R³, and R⁴ are each,independently of each other, H, a C₁₋₈ -alkyl group, a partly orcompletely fluorinated C₁₋₈ -alkyl group, or a C₃₋₈ -alkenyl group; R⁵is a C₁₋₈ -alkyl group, a partly or completely fluorinated C₁₋₈ -alkylgroup, or a C₁₋₃ -alkenyl group.